1. Field of the Invention
The present invention relates to printed antennas disposed on substrates, and particularly to a printed antenna disposed on a substrate in a wireless local area network (WLAN) device.
2. Description of Related Art
Wireless communication devices, such as mobile phones, wireless cards, and access points, radiate signals by use of electromagnetic waves. Thus, remote wireless communication devices can receive the signals without cables.
In a wireless communication device, an antenna is a key element for radiating and receiving radio frequency signals. Characteristics of the antenna, such as radiation efficiency, orientation, frequency band, and impedance matching, have a significant influence on the performance of the wireless communication device. Nowadays, there are two kinds of antennas: built-in antennas and external antennas. In contrast to the external antenna, the size of the built-in antenna is smaller, and the body of the built-in antenna is protected and not easily damaged. Thus, the built-in antenna is commonly employed in wireless communication devices. Common built-in antennas include low temperature co-fired ceramic antennas and printed antennas. The low temperature co-fired ceramic (LTCC) antenna has good performance at high frequencies and at high temperatures, but is expensive. The printed antenna has many types. A common type of printed antennas is a planar inverted-F antenna. Compared to low temperature co-fired ceramic antennas, planar inverted-F antennas are small, light, thin, and inexpensive. Accordingly, planar inverted-F antennas are being used more and more in wireless communication devices.
Referring to FIG. 5, a schematic diagram of a typical planar inverted-F antenna is shown. The planar inverted-F antenna includes a radiation part 10′ and a matching part 20′. The radiation part 10′ is for radiating and receiving radio frequency signals, and includes a first radiation segment 12′ and a second radiation segment 14′. The matching part 20′ is for impedance matching, and includes a first matching segment 22′ and a second matching segment 24′. The radiation part 10′ forms a resonator by the first radiation segment 12′ electrically connecting to the second radiation segment 14′. The radiation part 10′ is connected to the matching part 20′ at one side of a grounding plane 40′ to form the above-described planar inverted-F antenna.
Recently, more attention has been paid to developing small-sized and low-profile wireless communication devices. Antennas, as key elements of wireless communication devices, have to be miniaturized accordingly. Although, the above-described planar inverted-F antenna is smaller than an external antenna, the profile of the above-described planar inverted-F antenna cannot be reduced efficiently, and so the profile of the corresponding wireless communication device cannot be reduced efficiently either.
Therefore, a heretofore unaddressed need exists in the industry to overcome the aforementioned deficiencies and inadequacies.